1. Field of the Invention
The present invention generally relates to the production of chlorine dioxide and, more particularly, to novel apparatus and methods for increasing the efficiency of chlorine dioxide production utilizing metering pumps and a multiport reaction column under vacuum.
2. The Background
Chlorine was traditionally used as a chemical disinfectant to inactivate or chemically kill microorganisms in drinking water. Certain chlorinated, brominated or poly-substituted organic compounds may result, however, from the interaction of chlorine with natural organic matter in raw water supplies. Some of these compounds (i.e., trihalomethanes and the haloacetic acids formed by reactions between free chlorine and natural organic matter) have been linked with undesirable environmental side effects and potential long term health effects, such as cancer.
Chlorine dioxide, having the molecular formula of ClO2, has been found to not form these halogenated byproducts when it reacts with the same precursors as those produced with chlorine. Importantly, chlorine dioxide has been found to produce microbiologically safe water that is chemically disinfected without the high cost of ozone or causing the production of chlorine-related harmful halogenated byproducts. Thus, the bactericidal, fungicidal, algicidal, bleaching and deodorizing properties of chlorine dioxide are readily used by those skilled in the art for chemically disinfecting and treating water sources, without incurring the adverse environmental side effects that are associated with chlorine.
Unfortunately, chlorine dioxide is hazardous due to the unstable nature of gaseous chlorine dioxide when compressed, therefore chlorine dioxide does not lend itself to large scale factory production. It is necessary to produce chlorine dioxide on site rather than to produce it at a plant and ship it for usage when needed. As appreciated, chlorine dioxide generators and processes were developed by those skilled in the art to produce chlorine dioxide on site in the select quantities needed, thus allowing for limited production without the problems associated with large scale production, transportation and/or storage of the substance.
Although chlorine dioxide does produce inorganic byproducts (e.g., chlorine, chlorite, chlorate, chlorous acid, chloride ions and the like), these byproducts may be ultimately removed if proper procedures and protocols are followed. Whereas, the capability to effectively handle and remove disinfection byproducts produced by the process, the dramatic reduction of organic products produced as a result of the process, and the strong disinfection strength of chlorine dioxide makes it the better candidate for disinfecting and treating water sources. To this end, chlorine dioxide is presently used for disinfecting water, controlling taste and odor, color reduction, and for the oxidation of inorganic compounds like iron, manganese or sulfur compounds that generally detract from the aesthetic quality of the water.
Chlorine dioxide, acting as a disinfectant, may be used in both the pre-oxidation and the post-oxidation stages of water treatment. By adding chlorine dioxide in the pre-oxidation phase of the purification of surface water, the growth of bacteria and algae may be controlled in subsequent phases of treatment. Chlorine dioxide also acts as an oxidant (electron receiver) to colloidal substances, aiding in the coagulation process and improving the removal of turbidity.
In summary, chlorine dioxide may be used as a disinfectant and an oxidant in the treatment of drinking water. Chlorine dioxide may therefore be utilized in a variety of processes including a large number of bactericidal applications, especially in the field of water treatment in wastewater treatment facilities, odor abatement of raw sewage and the control of hydrogen sulfide in sewers.
The difficulties involved in the generation of chlorine dioxide can be demarcated into three specific groupings: (1) the production of chlorine dioxide in an appropriate carrier fluid; (2) the production of chlorine dioxide in the right concentration with the absence of unwanted byproducts or compounds; and (3) maximizing percent yield. Correspondingly, many prior art chlorine dioxide generation apparatus and methods have been developed by those skilled in the art in an effort to address many of the difficulties or disadvantageous associated with chlorine dioxide production.
For example, those skilled in the art developed a process for producing chlorine dioxide by reacting in a reaction vessel an alkali metal chlorate, a mineral acid, and methanol as a reducing agent in proportions to generate chlorine dioxide in a reaction medium that is maintained at a temperature of about 50° C. to about 100° C. and at an acidity within the interval from about 2 to about 11 N and subjected to a subatmospheric pressure. Water is evaporated and a mixture of chlorine dioxide, water vapor and gaseous byproducts is withdrawn from an evaporation region in the reaction vessel. The alkali metal sulphate is preferably precipitated in a crystallization region in the reaction vessel. The content of formic acid in the reaction vessel is increased by the addition of formic acid to a content of formic acid exceeding about 0.3 M. The gaseous byproducts are condensed to obtain formic acid and the content of formic acid in the reaction vessel is increased by recirculation of the condensate.
Another prior art apparatus and method was developed by those skilled in the art for forming an aqueous chlorine dioxide solution that includes reacting in a reaction vessel an acid reaction solution containing a hydroxy carboxylic acid and a companion acid with an alkali metal salt of a chlorite ion. The hydroxy carboxylic acid serves to temporarily transfer chlorine from and does not form a salt with the alkali metal salt of the chlorite ion. The apparatus includes a stripping unit whereby product solution is contacted with an inert gas to produce a product gas, and an absorbing unit whereby the product gas is contacted with an aqueous medium to produce an aqueous solution of chlorine dioxide.
Of the above listed challenges associated with prior art apparatus and methods for chlorine dioxide generation, perhaps the most difficult to solve is maximizing percent yield. Economics dictate that the profit of a production process is maximized when all the inputs are used to completion without excess or waste, while requiring the shortest amount of time possible. In chemical reactions, the inputs are referred to as reactants, the end products are referred to simply as the products.
Those skilled in the art refer to theoretical yield as the maximum possible generation of a product with a given quantity of reactants. In order to reach the theoretical yield, all the molecules of one reactant must find a complementary molecule of a differing reactant and combine in such a way to form the desired product. In the real world, it is very difficult to ensure that every reactant molecule comes in contact with a complement, wherein the yield of the desired product is generally referred to as the actual yield.
Percent yield may be defined as the ratio of actual yield to the theoretical yield. Thus, in an efficient chemical reaction, the actual yield approaches the theoretical yield and the resulting percent yield is high. In order to increase percent yield, it is common practice to add an excess of one reactant, thus greatly increasing the probability that all of the accompanying limiting reactant is consumed. However, this practice may be undesirable for two reasons. First, after the limiting reactant has been consumed, the excess reactant is wasted and can not be readily recovered. Second, the reactant in excess may adversely affect the characteristics of the final solution. For example, if chlorine were the excess reactant, its presence would result in the environmental side effects that were meant to be avoided. Thus, it would be an advancement in the art to develop a chlorine dioxide generation apparatus and methods that produces a high percent yield without introducing significant excesses of one or more of the reactants.
Time is also an important factor in creating an economical production process. The faster the progression of the production process, the greater the amount of product that can be produced in a given amount of time. However, an increase in the time allotted for a reaction to occur, promotes a higher percent yield. The reasoning is obvious, the more time the reactant molecules have to move about, the more probable that they will encounter a complement and react. Therefore, in order to reach an optimal economic production, there must be a compromise between the time allotted for the reaction and the resulting percent yield. To this end, it would be an advancement in the art to create a chlorine dioxide generation apparatus and methods that maximize reactant interaction thereby substantially shortening the amount of time that is required to reach optimal economic production.
Several apparatus and methods of the prior art have been directed at increasing the percent yield in chlorine dioxide generation. One such prior art chlorine dioxide generation apparatus utilizes vacuum chemical feed systems. A significant disadvantage with these types of prior art vacuum chemical feed systems is that there is a low emphasis on precise mixture of chemicals, volumetrically or symmetrically. It would therefore be an advancement in the art to have a chlorine dioxide generator that meters a precise volume of reactant chemicals synchronized and combined through internal ports with dimensions calculated to exact collision timing within a reaction column and then exiting the apparatus via a single output port. Such a device is disclosed herein.